The studies in this proposal address the specific role that signaling pathways play in regulation of bile acid biosynthetic enzymes, specifically the enzyme cholesterol 7 alpha-hydroxylase (CYP7A1), the rate-limiting enzyme in the neutral pathway of bile acid biosynthesis. Recent findings from our laboratory provide strong evidence that activation of the c-Jun N-terminal Kinase (JNK) pathway by bile acids plays a pivotal role in regulation of CYP7A1 in primary rat hepatocytes. However, the molecular events by which bile acids activate this pathway have not yet been fully elucidated, but may have important implications in the pathogenesis of hypercholesterolemia and cholestatic liver diseases. It is proposed that interplay of ceramide and FAS within outer membrane lipid rafts is capable of regulating CYP7A1 through JNK activation. The objectives of this application are to (1) determine the mechanism(s) of activation of the JNK pathway by bile acids by defining the role of the FAS receptor in the activation of JNK in primary hepatocytes, (2) investigate the involvement of sphingomyelinases and ceramide in activation of the FAS receptor by bile acids, (3) determine whether the mechanism(s) of in vitro regulation of CYP7A1 by bile acids also apply in vivo, using FAS and acidic sphingomyelinase knock-out mice. An integrative approach combining kinase assays, ceramide measurements, fluorescence imaging, serum lipid analysis, and other molecular biology techniques will be applied to the proposed studies. Studies will be performed at Virginia Commonwealth University's-Medical College of Virginia Campus. The Department of Microbiology and Immunology and the Liver Centre at VCU are fully committed to support this research endeavor and to further develop the candidate's research career by providing the protected time, resources, and continuing research educational opportunities. This will enable the candidate to achieve her long term career goals of forming a fundamental understanding of bile acid-mediated signaling to serve as a basis for the development of effective therapies to reduce serum cholesterol levels and limit cholestasis-associated liver damage, and to develop an independent and successful research career.